Intestinal epithelial cells are a major site of contact between the host and microbes, microbial products, and other environmental agents that cause epithelial cell injury. Our long-term objective is to define the mechanisms by which intestinal epithelial cells play a role in host mucosal defense by signaling the onset of innate and adaptive immune and inflammatory responses in the intestinal mucosa. In vitro studies indicate the importance of the transcription factor NF-kappaB as a central regulator of the intestinal epithelial cell response to microbial infection, yet little is known regarding the functional importance in vivo of epithelial cell NF-kappaB for mucosal innate immunity and epithelial cell survival. Studies in Specific Aim 1 will determine the functional importance of intestinal epithelial cell NF-kappaB in vivo by testing the hypothesis that activation of NF-kappaB in intestinal epithelial cells has a key role in signaling the onset of the mucosal inflammation in response to microbial and chemical injury, and in protecting epithelial cells from undergoing apoptosis in response to gamma radiation. These in vivo studies will use mice in which Cre recombinase under the control of the villin promoter was used to generate progeny with a conditional intestinal epithelial cell knockout of the beta subunit of the IkappaB kinase (IKK) that is essential for signal induced activation of NF-kappaB. Specific Aim 2 will study the importance of epithelial cell NF-kappaB for epithelial cell migration in an in vitro model of epithelial cell restitution. Epithelial cell restitution is the process wherebyintestinal epithelial cells migrate to seal a superficial wound in the early period following epithelial cell injury. In preliminary studies we discovered that NF-kappaB is activated at the wound edge and that NF-kappaB is essential for subsequent epithelial cell migration. Studies in Aim 2 will further test the hypothesis that NF-kappaB plays a central role in regulating epithelial cell migration following epithelial cell wound injury. The proposed studies focus on the proximal signaling mechanisms that lead to NF-kappaB activation following epithelial cell wound injury and the NF-kappaB responsive genes that play a central role in this model of epithelial cell injury. The proposed studies have marked significance for understanding the mechanisms that initiate and regulate intestinal mucosal inflammation and epithelial cell survival, and for elucidating mechanisms that are important for re-epithelialization of mucosal surfaces during microbial or toxic intestinal injuries and in inflammatory bowel diseases and celiac disease.